This invention relates to a heating element for use in a fluid heater. More specifically, this invention relates to a non-metallic heating element that is not susceptible to corrosion. This heating element may be inside the housing of a fluid heater and/or constitute the pipes that input fluid to and output fluid from the heater.
In the prior art, the storage-type fluid heater is comprised of a metallic or the less common plastic container. This describes the vast majority of vessels that are used for the purpose of heating a fluid. The source energy to raise the temperature of the fluid, within the container, to its desired predetermined level, the temperature setpoint, may be electric, combustible petroleum, or combustible gas. Regardless of the energy source the prior art has shown that metal(s) have been used to contain and apply heat to the fluid. This use of metal in constant contact with water has led to negative results. Specifically, the metallic heating elements are subject to failure due to corrosion. This corrosion is facilitated by the mineral build up within the base of the metallic storage tank as well as direct adherence to the internal metallic heating elements. The mineral build up is caused by the continuous heating of a fluid, such as water, under relatively low pressures and then having that hot fluid remain stagnant. This internal state of the fluid heating tank allows minerals to precipitate out of the fluid, to build up on the base of the tank, and to form onto the protruding internal electrical heating elements.
Fluid heaters that are heated by natural gas typically comprise a vertical, cylindrical tank having a centrally located gas flue passing vertically through the tank. The radial flame gas burner is located below the bottom of the metallic tank. This burner heats the water in the tank. Additionally heat is transferred to water in the tank from hot combustion gasses produced by the burner passing upward through the gas flue. Flue baffles and similar apparatuses are commonly employed in the gas flue for improving heat transfer from the combustion gases to the water in the tank. Combustion gases are exhausted from the gas flue near the top of the tank.
Fluid heaters that are electrically heated generally comprise a vertical cylindrical metallic or in this case a non-metallic tank having one or more electrical resistance heating elements mounted at intermediate elevations in the water tank. Heat is exchanged between the metallic heating elements and water in the tank.
Prior art attempts to resist corrosion included the placement of an anode within the tank. The anode is a metal rod usually made of magnesium or aluminum. Electrolysis eats away the metal anode instead of the other metal (heating elements or walls) of the tank. The benefit of this is limited, however, because once the anode is exhausted, the tank itself begins to corrode. Another deficiency found in prior art electric type fluid heaters is a reduction in heating efficiency due to the mineral content of the water. When water is heated under pressure, minerals will precipitate out of the water and adhere to the electric heating elements thus reducing their efficiency and eventually promoting their failure. Those deposits will also form into larger crystals and remain on the bottom of the tank; this is particularly troublesome for flame producing heaters, since the heat must transfer through large deposit layers.
The average life of a residential storage type water heater is about 13 years. The corrosion of the heating elements and tank of the heater can decrease the operating time and negatively impact performance during its functioning life.
The difficulties and limitations suggested in the preceding are not intended to be exhaustive, but rather are among many which demonstrate that although significant attention has been devoted to decreasing the amount of corrosion within fluid heaters and their resulting decreased function, the prior attempts do not satisfy the need for long term stability of the fluid heater.